Local Anesthetic Injections for the Short-Term Treatment of Head and Neck Myofascial Pain Syndrome: A Systematic Review with Meta-Analysis

Aims: To evaluate the effectiveness of local anesthetic trigger point injections in adults with myofascial pain syndrome (MPS) in the head, neck, and shoulder regions compared to dry needling, placebo, and other interventions. Methods: Randomized controlled trials using local anesthetic injections in adults diagnosed with MPS were included. The Cochrane Library, MEDLINE via PubMed, Web of Science, and EMBASE libraries were searched. The primary outcome was pain measured with a 0 to 10 visual analog scale (VAS). Secondary outcomes included pain threshold, range of cervical motion, depression scale, and pressure pain intensity (PPI) score. Risk of bias was analyzed based on Cochrane's handbook. Results: The initial search strategy yielded 324 unduplicated references up to April 1, 2018. A total of 15 RCTs were included, with 884 adult patients diagnosed with MPS. Meta-analysis showed a significant improvement in VAS pain scale of 1.585 units at 1 to 4 weeks in the local anesthetic group compared to the dry needling group (95% confidence interval -2.926 to -.245; P = .020). However, when only including double-blinded studies, the effect was not statistically significant (P = .331). There was also a significant improvement in pain of 0.767 units with local anesthetic at 2 to 8 weeks compared to placebo (95% confidence interval -1.324 to -0.210; P = .007). No statistically significant differences were found in other secondary outcomes between local anesthetic and all other interventions. Conclusion: Though local anesthetics provided a significant improvement in pain compared to dry needling, evidence was of low quality, and sensitivity analyses including only double-blinded studies provided no statistically significant difference. Additional studies are needed to confirm these results. Palabras clave: dry needling, local anesthetic, meta-analysis, myofascial pain, myofascial trigger points, systematic review, visual analog scale